A wide variety of mental and physical processes are controlled or influenced by neural activity in particular regions of the brain. In some areas of the brain, such as in the sensory or motor cortices, the organization of the brain resembles a map of the human body; this is referred to as the “somatotopic organization of the brain.” There are several other areas of the brain that appear to have distinct functions that are located in specific regions of the brain in most individuals. For example, areas of the occipital lobes relate to vision, regions of the left inferior frontal lobes relate to language in the majority of people, and regions of the cerebral cortex appear to be consistently involved with conscious awareness, memory, and intellect. This type of location-specific functional organization of the brain, in which discrete locations of the brain are statistically likely to control particular mental or physical functions in normal individuals, is herein referred to as the “functional organization of the brain.”
Many problems or abnormalities with body functions can be caused by damage, disease and/or disorders of the brain. A stroke, for example, is one very common condition that damages the brain. Strokes are generally caused by emboli (e.g., obstruction of a vessel), hemorrhages (e.g., rupture of a vessel), or thrombi (e.g., clotting) in the vascular system of a specific region of the cortex, which in turn generally causes a loss or impairment of a neural function (e.g., neural functions related to face muscles, limbs, speech, etc.). Stroke patients are typically treated using physical therapy to rehabilitate the loss of function of a limb or another affected body part. For most patients, little can be done to improve the function of the affected limb beyond the recovery that occurs naturally without intervention.
One existing physical therapy technique for treating stroke patients constrains or restrains the use of a working body part of the patient to force the patient to use the affected body part. For example, the loss of use of a limb is treated by restraining the other limb. Although this type of physical therapy has shown some experimental efficacy, it is expensive, time-consuming and little-used. Stroke patients can also be treated using physical therapy plus adjunctive therapies. For example, some types of drugs, including amphetamines, increase the activation of neurons in general. These drugs also appear to enhance neural networks. However, these drugs may have limited efficacy because the mechanisms by which they operate are very non-selective and they cannot be delivered in high concentrations directly at the site where they are needed. Still another approach is to apply electrical stimulation to the brain to promote the recovery of functionality lost as a result of a stroke. While this approach has been generally effective, it has not adequately addressed all stroke symptoms.
In addition to the motor-related symptoms described above, stroke patients may also suffer from cognitive defects. For example, patients may suffer from neglect, a defect that causes patients to lose cognizance of portions of their surroundings and/or themselves. In other cases, patients may suffer from other cognitive defects, such as memory loss or loss of reasoning ability, in connection with a stroke or other event that causes neural damage. While electromagnetic stimulation has been proposed generally to address cognitive defects, the application of such techniques may in some cases be difficult because, unlike motor neurons, which can immediately indicate activation by a corresponding muscle action, cognitive and other non-motor neurons typically do not provide such a readily discernable indication of activation. Accordingly, there is a need to improve the manner in which stimulation is applied to cognitive and other non-motor neurons.